1. Field of the Invention
The invention relates to a book scanner with enhanced edge image quality, and more particular to a book scanner having a bent lighting device to compensate for the edge brightness of the lighting device.
2. Description of the Related Art
The flat-bed image scanner has been widely used as a peripheral equipment for computers. It can scan the text of documents, magazines, books, graphs, etc. or pictures for further processing in the computer.
A flat-bed scanner is composed of an optical reading unit, a driving unit, a picture processing circuit, a transparent scanning window and a frame. The development trend today is to make the scanner lighter, thinner, shorter and smaller, so that the scanner can occupy less space.
FIG. 1 shows a linear light source 101 of a conventional design. Element 11 is the frame, over which a scanning window 12 rests. The scanning window 12 has an effective scanning area 12a. The area 12b is an ineffective scanning area because the area has poorer lighting due to the end section construction of a typical fluorescent lamp. This area 12b is used for connecting the scanning window 12 with the frame 11.
FIG. 2 shows the effective illumination area of the linear light source of the conventional design. The drawback of the linear light source is that the illumination of the lamp 101 at the two ends 101b is weaker than the central portion of the light source. The weaker lighting areas cause poorer illumination at the two edges of the exposed document and degrade the quality of the scanned image. Only the central portion 101a of the linear lamp 101 can scan the scanning window effectively, maintaining a high quality image. To solve the poor illumination at the two ends of the lamp, a conventional practice is to elongate the lamp. The elongated length makes the poorly illuminated region 101b lie outside the effective illumination region 101a. The drawback of this structure is the extension of the linear lamp, thus increasing the volume of the scanning equipment to accommodate the increased length of the lamp. Although the extension is not much, the frame of the scanner must be increased substantially in terms of volume and weight.
In U.S. Pat. No. 5,475,505, a U-shaped lighting tube or an Ω-shaped lighting tube is used to solve the poor end zone illumination problem. In the U-shaped lighting tube design, two parallel tubes are connected at one end but opened at the other end. Although this design can reduce the size of the scanning unit and improve the quality of illumination at the connected end of the tubes, the quality of illumination at the other open end of the tubes is not improved. In the U.S. Pat. No. 5,475,505, the open end of the tube is extended outward into Ω-shape. With this design, the poorly illuminated end is extended to increase the illumination at that end. However, such a design requires more tube material. The function of this invention is to increase the illumination of the two poorly illuminated ends with less material.
Consequently, the lamp tube used in the conventional scanner usually has uneven brightness distribution because the brightness at the middle of the lamp tube is higher and evener while the brightness at two ends of the tube is low. Hence, using the lamp tube with uneven brightness to scan the document cannot obtain good scan results. In order to solve this problem, the above-mentioned U-shaped lamp tube has been proposed to compensate for the edge brightness of the lamp tube.
FIG. 3 is a schematic illustration showing that the U-shaped lamp tube is used to compensate for the edge brightness. As shown in FIG. 3, the U-shaped lamp tube 110 of the scanner has a bent portion 112, which is correspondingly located around the edge of the document 100 and fixed to the scanning module 140 by a fixer 120. Because extra light rays may compensate for the edge brightness of the document 100, the scan quality can be enhanced.
FIG. 4 is a partially schematic illustration showing that the lamp tube of FIG. 3 is applied to a book scanner. As shown in FIG. 4, the housing 150 of the book scanner 130 typically has a housing platen 152 for supporting the book together with the transparent platen 160. In addition, in order to maintain a fixed amount of brightness of the lamp tube to be illuminated on the book, the distance from the lamp tube 110 to the transparent platen 160 usually cannot be too large. Consequently, even if the U-shaped lamp tube 110 contacts the housing platen 152, sufficient light rays around the binding edge of the book still cannot be provided because the slanting housing platen 152 restricts the left extensible range of the U-shaped lamp tube 110 in FIG. 4. In addition, the U-shaped lamp tube 110 cannot be easily manufactured, so its cost is high. In addition, the fixer 120 for fixing the U-shaped lamp tube 110 to the scanning module 140 usually has a high price and a poor fixing effect, or the fixer 120 may shield a portion of the light rays and thus influence the brightness compensation.
The compensation technology of the lamp tube brightness may be found in U.S. Pat. Nos. 5,475,505; 5,768,663; 5,950,053; and 6,133,580, wherein the disclosed lamp tubes have many types for compensating for the edge brightness. However, these lamp tubes and the configurations thereof may encounter the above-mentioned problems in use.
Therefore, it is an important subject of the invention to provide a book scanner capable of compensating for the edge brightness when scanning the book.